Neuralgias, such as trigeminal, sphenopalatine, and occipital neuralgias may start at any age, although trigeminal neuralgia is more common among the elderly. From a pathophysiological standpoint, pain arising due to neuralgias always originates from, and is transmitted by, the involved nerve. Accordingly, neuralgias may be caused by direct injury to nerves in the form of trauma, infection (e.g., herpes), neuroma formation or demyelination. Pain arising due to neuralgia may be brief and paroxysmal or continuous, and numerous attacks may occur throughout the day. Neuralgias do not feature seasonal or diurnal patterns in the onset of pain. Trigeminal neuralgia often has an associated “trigger zone” on the face, which can trigger the onset of the pain. Sphenopalatine neuralgia often has autonomic features, which are not commonly found in other neuralgias. In occipital neuralgia, the occipital nerve is usually tender to palpation and pain can be manifested anywhere along the course of the nerve.
Historically, neuralgias have been treated using medication, invasive procedures and, rarely, electrical stimulation of cranial nerves. Newer techniques have been developed for treating a variety of neurological disorders including electrical stimulation of cranial nerves, such as the glossopharangeal, vagus or trigeminal nerves. U.S. Pat. No. 5,540,734 to Zabara, for example, describes a suggested therapeutic modality for a variety of medical, psychiatric, and neurological disorders in which modulating electrical signals are applied to either or both of the trigeminal and glossopharyngeal nerves using electrodes. The principle behind these approaches is to disrupt or modulate abnormal neuronal transmissions in the nervous system through the application of electrical signals.
The use of medications to treat the above-described conditions can result in systemic side-effects of wide-ranging severity. Invasive techniques used to destroy tissues, such as lesioning, resecting, freezing or burning, are typically non-reversible, and the treatment cannot be adjusted once applied. Destruction of the tissue may itself lead to significant side effects, such as deafferentation pain.